Today, we are announcing support for DNS resolution of hostnames where instances have private IP address outside of the RFC 1918 space. With this support now available natively in EC2 DNS, customers do not have to run custom DNS servers if the CIDR range for their VPC is outside of the RFC 1918 range. Previously, private DNS hostname resolution was supported only for RFC-1918 assigned private address ranges (10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16).

The feature is automatically turned on for all new VPCs by default. VPCs that have address ranges outside of the RFC 1918 space will see that now their private IP addresses resolve to internal DNS hostname of ip-aa-bb-cc-dd.<region>.compute.internal format (where aa.bb.cc.dd is the reverse lookup address). For more information, see ‘Using DNS with your VPC’.